Oxidation of methane to methanol with hydrogen peroxide using supported gold-palladium alloy nanoparticles

Article abstract of DOI:10.1002/anie.201207717

Direct and selective: Supported gold-palladium nanoparticles are active for the oxidation of methane, giving a high selectivity for the formation of methyl hydroperoxide and methanol, using hydrogen peroxide as the oxidant (see picture). The optimal methanol selectivity is achieved by performing the reaction in the presence of hydrogen peroxide that has been generated in situ from hydrogen and oxygen. Copyright

Full text of DOI:10.1002/anie.201207717

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Angewandte
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DOI: 10.1002/anie.201207717
Oxidation of Methane
Oxidation of Methane to Methanol with Hydrogen Peroxide Using
Supported Gold–Palladium Alloy Nanoparticles**
Mohd Hasbi Ab Rahim, Michael M. Forde, Robert L. Jenkins, Ceri Hammond, Qian He,
Nikolaos Dimitratos, Jose Antonio Lopez-Sanchez, Albert F. Carley, Stuart H. Taylor,
David J. Willock, Damien M. Murphy, Christopher J. Kiely, and Graham J. Hutchings*
The direct conversion of methane to methanol remains a key
challenge. The current commercial production of methanol
from methane has been fine-tuned over many decades of
operation and gives a high selectivity for the formation of
methanol, but involves a high energy input two-stage process.
Direct conversion of methane to methanol in a single step
would clearly provide many advantages.[1] Catalysts identified
that operate at high temperature can give a high methanol
selectivity at low conversion.[2] Using milder reaction con-
ditions catalysts do not give closed catalytic cycles.[3–12]
Recently we have shown that CuFe-ZSM-5 is an effective
catalyst for the conversion of methane to methanol with
a closed catalytic cycle when H2O2 was used as an oxidant.[13]
This has prompted us to investigate the use of other catalysts
with this oxidant. We have previously shown that supported
Au-Pd nanoparticles are highly effective catalysts for the
direct synthesis of H2O2,[14] the oxidation of alcohols,[15] and
In a typical reaction, the oxidation of methane is
performed in liquid phase using an autoclave reactor with
water as solvent and H2O2 as oxidant. Initially, we inves-
tigated the activity of supported Au-Pd/TiO2 prepared by sol
immobilization[16] but found high H2O2 decomposition
(Table 1, entry 1). We considered that the high H2O2 decom-
position rate which was facilitated by the small size and
metallic oxidation state of the AuPd nanoparticles. Therefore,
we used Au-Pd catalysts prepared by incipient wetness (IW),
as they have been shown to be effective in the direct synthesis
of H2O2 with low decomposition/hydrogenation rates.[14]
Using 1 wt% Au-Pd/TiO2 (IW) the turnover frequency
(TOF) for methane oxidation was increased by a factor of
two and about 58% of the oxidant remained after reaction, as
opposed to the complete decomposition of H2O2 that was
observed with the sol immobilization catalyst (Table 1,
entries 1 and 2). The selectivity to methanol was lower in
the case of the IW catalyst, this being due to a higher
selectivity to methyl hydroperoxide.
Encouraged by these results, we examined the effect of
temperature on the catalytic activity (Table 1, entries 3–5)
since it has been reported that HAuCl4 (and other metal
chlorides) can be very active for the aqueous phase oxidation
of methane using hydrogen peroxide at 908C.[17] HCOOH and
CO2 were the main products of the high temperature
homogeneous oxidation,[20] accompanied by metal minerali-
zation, whilst there was a marked reduction in catalytic
activity at 508C (see Table S1 in the Supporting Information).
For the heterogeneously catalyzed reaction, as the temper-
ature was increased the catalytic productivity improved
markedly. The maximum TOF (ca. 25 hꢀ1) and the highest
methanol selectivity under these conditions (19%), was
achieved at 908C (Table 1, entry 3). Remarkably, methanol
was stable at 908C under our reaction conditions, but we
noted that methyl hydroperoxide was the major reaction
product in all cases. Sꢀss-Fink and co-workers[21] have shown
that methyl hydroperoxide is transformed to formaldehyde
and formic acid at temperatures above 408C in the absence of
a catalyst. However, at the temperatures we employed (30–
908C) these particular products were not observed, suggesting
that the formation of methyl hydroperoxide and methanol is
due to the presence of the Au-Pd catalyst.
[16]
ꢀ
the oxidation of primary C H bonds in toluene.
We
consider that all these reactions are linked by the formation
of a hydroperoxy intermediate from dioxygen. We considered
that a hydroperoxy species may be effective for the oxidation,
since it is known that H2O2 or tert-butyl hydroperoxide
(TBHP) have been used to oxidize methane.[17–19] In view of
this we have used hydrogen peroxide as oxidant and here we
show that Au-Pd supported nanoparticles are active for the
oxidation of methane, giving a high selectivity for the
formation of methanol, especially when the reaction is carried
out in the presence of hydrogen peroxide generated in situ
from hydrogen and oxygen.
[*] Dr. M. H. Ab Rahim,[+] Dr. M. M. Forde, Dr. R. L. Jenkins,
Dr. C. Hammond, Dr. N. Dimitratos, Dr. J. A. Lopez-Sanchez,
Dr. A. F. Carley, Dr. S. H. Taylor, Dr. D. J. Willock, Dr. D. M. Murphy,
Prof. G. J. Hutchings
Cardiff Catalysis Institute, Cardiff University
Main Building, Park Place CF103AT Cardiff (UK)
E-mail: hutch@cardiff.ac.uk
Dr. Q. He, Prof. C. J. Kiely
Department of Materials Science and Engineering
Leigh University
5 East Packer Avenue, Bethlehem, PA 18015-3195 (USA)
[+] Current address: Faculty of Industrial Sciences & Technology
University Malaysia Pahang
We reasoned that the low methanol selectivity could be
linked to the low metal loading (7.24 ꢁ 10ꢀ7 mol) employed in
these reactions and therefore tested 2.5 wt% Au-2.5 wt% Pd/
TiO2 (IW), a material which has been well characterized in
a number of previous publications and so the results will not
Lebuhraya Tun Razak, 26300, Kuantan, Pahang (Malaysia)
[**] This work formed part of the Methane Challenge. The Dow Chemical
Company is thanked for their financial support.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201207717.
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Table 1: Comparative catalytic activity of various Au-based catalysts for the liquid-phase oxidation of methane, with hydrogen peroxide either 1) added
as co-reactant or 2) generated in situ from a H2/O2 mixture under mild conditions.[a]
Metal[b] T [oC] Oxidant
[wt%]
Products [mmol]
Oxy.
sel.[e]
[%]
CH3OH
sel.[f] [%] [molkgcatꢀ1 hꢀ1
Total prod.[g]
TOF[h] H2O2
[hꢀ1
[mmol]
[i]
Entry Catalyst
]
]
CH3OH[c] HCOOH[c] MeOOH[c] CO2
[g]
[d]
1
AuPd/TiO2 1.0
50
H2O2
0.60
0
0
0.41
59.4
59.4
0.10
2.79 <15
(sol im.)
2
3
4
5
6
7
8
AuPd/TiO2 1.0
AuPd/TiO2 1.0
AuPd/TiO2 1.0
AuPd/TiO2 1.0
AuPd/TiO2 5.0
AuPd/TiO2 5.0
50
90
70
30
50
2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2/O2
0.30
1.84
0.66
0.19
1.89
1.31
0.12
0
0
0
0
0
0
0
1.82
6.39
3.90
1.09
1.57
1.40
0
0.36
1.08
0.47
0.28
0.37
0.19
0.54
85.4
88.4
88.9
82.6
90.3
93.4
18.2
12.1
19.8
12.9
12.2
49.3
45.2
18.2
0.50
1.86
1.03
0.31
0.28
0.21
0.009
6.85 2894
25.72 278
14.17 1595
4.28 3988
0.77 383
0.58 4471
0.024 33
Au/
5.0
50
TiO2 +Pd/
TiO2*
9
Au/
5.0
50
H2/O2
0.81
0
0
0.58
58.3
58.3
0.059
0.162 21
TiO2 +Pd/
TiO2**
10
11
12
13
AuPd/TiO2 5.0
AuPd/TiO2 5.0
AuPd/TiO2 5.0
AuPd/TiO2 5.0
50
2
70
50
H2/O2
H2/O2
H2/O2
NADH/ 4.48
O2
1.31
0.26
0.81
0
0
0
0
0.29
0.47
0.1
0
0.32
0.15
0.11
0.54
83.3
83.0
89.2
89.2
68.2
29.5
79.4
89.2
0.116
0.053
0.059
0.081
0.320 56
0.146 124
0.164 29
0.224 n.d.
[a] Typical reaction conditions: time: 30 minutes, pressure of CH4: 30.5 bar, stirring rate: 1500 rpm, entries 1–5 catalyst: 7.24ꢀ10ꢀ7 mol of metals
equal to 10 mg of solid catalysts, entries 6–13 catalyst: 1.0ꢀ10ꢀ5 mol of metals equal to 28 mg for solid catalysts, volume: 10 mL of H2O. [H2O2]: 0.5m,
H2/O2 gases mixture: 0.86% H2/1.72% O2/75.86% CH4/21.55% N2. *Reaction of a physical mixture comprising 2.5 wt% Au/TiO2 and 2.5 wt% Pd/
TiO2 at a 1:1 weight ratio for 28 mg of the total catalyst. **Reaction of a physical mixture comprising 2.5 wt% Au/TiO2 and 2.5 wt% Pd/TiO2 at a 1:1
molar metal ratio for 28 mg of the total catalyst. All solid catalysts have been prepared by incipient wetness and calcined at 4008C for 3 h in static air,
except for entry 1. n.d.=not determined. [b] The weight ratio Au:Pd in a bimetallic catalyst is 1:1. [c] Analyzed by 1H NMR spectroscopy with 1% TMS
in CDCl3 internal standard. [d] Analyzed by a gas chromatography/flame ionization detection. Values obtained from a CO2 calibration curve.
[e] Calculated as moles(oxygenates)/moles(total products)100. [f] Calculated as moles(MeOH)/moles(total products)100. [g] Calculated as
moles(products)/weight(catalyst)/time. [h] Calculated as moles(products)/moles(metal catalyst)/time. [i] Remaining H2O2 assayed by Ce+4(aq.)
titration. sol im.: sol immobilization; oxy.: oxygenate; sel.: selectivity, and prod.: productivity.
be repeated here.[14,15] For completeness, detailed scanning
transmission electron microscopy characterization of the
1 wt% Au-Pd/TiO2 (IW) catalyst has also been performed
as shown in Figure 1. Many of the metal particles were found
to be in the 5–20 nm size range, (Figure 1a,b), and were
confirmed to be AuPd alloys that were consistently enriched
in Au compared to the nominal composition (Figure 1c).
Furthermore a Pd-rich shell/Au-rich core morphology would
be detected in many of these 5–20 nm particles by virtue of
their characteristic z-contrast in the high-angle annular dark-
field (HAADF) imaging mode (Figure 1b). Higher magnifi-
cation HAADF images also showed the existence of a sig-
nificant population of 1–2 nm particles and subnanometer
clusters (Figure 1d,e), which X-ray energy dispersive spec-
troscopy (XEDS) analysis (Figure 1 f) showed to be Pd-rich in
character. Furthermore, some occasional 100–200 nm parti-
cles which were Au-rich could also be found when the sample
was examined by SEM (Figure S1), indicating that the initial
dispersion of the Au precursor was not perfect. The particle
size distribution and characteristic particle size/composition
trend were found to be similar for both the 0.5 wt% Au-
0.5 wt% Pd/TiO2 (IW) and the 2.5 wt% Au-2.5 wt% Pd/TiO2
(IW) catalyst materials, with the only significant difference
being the obviously higher overall metal loading in the latter
sample.
The 5 wt% metal catalyst gives a higher methanol
selectivity than that observed with the 1 wt% Au-Pd/TiO2
(IW) catalyst (i.e. 49% versus 14%, Table 1, entries 6 versus
2), but a similar overall oxygenate selectivity. The overall
catalyst productivity is lower for the 5wt% metal-loaded
catalyst and this is linked to the high H2O2 decomposition
rate, as is the case for the sol immobilization catalyst. Hence
we investigated the 5 wt% catalyst at a lower temperature
(28C) and observed methane activation with 93% oxygenate
selectivity (45% to methanol), low H2O2 usage (about 90%
left after reaction) and a similar rate to higher temperature
reactions (Table 1, entry 7). Changing the weight percent
ratio of Au:Pd alters the conversion and product distribution
(Table S2).
As titania is well-known for activating hydrogen peroxide
to produce surface-stabilized peroxo- or hydroperoxo species
(TiO2-O2ꢀ and Ti-OOH),[22] we performed experiments using
TiO2 as catalyst. No products were observed indicating that
TiO2 cannot oxidize CH4 in the absence of the AuPd
component of the catalyst. (Table S2). However, the identity
of the support may affect the conversion and product
distribution for AuPd catalysts (Table S3). In agreement
with previously reported data,[13,18] higher CH4 pressures and
increasing the initial concentration of H2O2 have the clear
effect of increasing the total oxygenates produced with no
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Figure 2. a) Time-on-line plot of methane oxidation with addition of
~
H2O2 in the presence of a 1 wt%AuPd/TiO2 (IW) catalyst. Key:
Figure 1. Representative scanning transmission electron microscopy
(STEM) HAADF images and corresponding STEM-XEDS spectra from
the 1 wt%AuPd/TiO2 (IW) sample. a,b) Low and higher magnification
HAADF images showing metal particles in the 5–20 nm size range.
c) The XEDS spectrum obtained from the 10 nm particle shown in (b)
which indicates that it is a Au-Pd alloy that is enriched in Au compared
to the nominal composition. A distinct Au-rich core/Pd-rich shell
morphology can also be deduced from image (b) as the particle
exhibits significantly fainter contrast at its extremity. d,e) Even higher
magnification HAADF images showing a significant population of 1–
2 nm particles and subnanometer clusters co-existing on the TiO2
support surface. f) The XEDS spectrum of the particle highlighted in
(e) suggests that these smaller species are very Pd-rich.
^
*
selectivity to methyl hydroperoxide, selectivity to methanol,
selectivity to carbon dioxide, x methane conversion. Reaction condi-
tions: PðCH ¼30.5 bar, [H2O2]=0.5m, T=508C, stirring
4Þ
rate=1500 rpm, and catalyst mass=10 mg. b) 1H NMR spectrum of
the reaction filtrate collected when using a solution initially spiked
with 13CH3OOH in a typical reaction using 5 wt%Au-Pd/TiO2 (IW) and
pure 12CH4.
We considered that it was important to establish the
reaction pathway and probe mechanistic aspects of this
catalyzed reaction. To this end, we first synthesized 13C-
oxygenated products using 13CH4 to verify that all of the
observed products were derived from methane. We also
introduced a known amount of the isotopically labelled
13CH3OOH into a typical reaction using a 5 wt%Au-Pd/TiO2
(IW) catalyst and a pure 12CH4 gas feed. The 1H NMR
analysis of the post-reaction mixture showed the presence of
13CH3OH and 12CH3OH (Figure 2b). In the absence of the
catalyst, however, no 13CH3OH was observed. As pure 12CH4
was used in the second step, we confirmed that 13CH3OOH is
transformed into 13CH3OH by the Au-Pd catalyst as the
reaction proceeds. Additionally, when methanol is used as
a substrate only 29% is oxidized at 508C, mainly to CO2, but
we observe that formaldehyde and formic acid undergo facile
oxidation to CO2 (Table S4).
appreciable loss in methanol selectivity over the ranges
studied (Figures S2 and S3). Furthermore, prolonging the
reaction time at 508C increased the methanol formation to
give a maximum selectivity of about 50% (Figure 2a). We
also noted that methyl hydroperoxide, recently identified in
our work with ZSM-5 as the primary reaction product of
methane oxidation,[13] is also present in the Au-Pd system.
This time-on-line study clearly demonstrates that methyl
hydroperoxide is the primary reaction product being sub-
sequently transformed to methanol and CO2 in the presence
of the catalyst, but significantly without the generation of
formic acid at the concentrations that we have employed.
Hence these data support the hypothesis that both the
oxidation of methane and the subsequent oxidation of the
primary reaction product are mediated by the Au-Pd surface.
To investigate the nature of the oxidation we carried out
electron paramagnetic resonance (EPR) studies under cata-
lytic reaction conditions. 5,5’-Dimethyl-1-pyrroline-N-oxide
(DMPO), was selected as a radical trap as it is routinely used
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to detect a number of radical species which may be produced
(i.e. CCH3. COCH3, COH, COOH, O2 C). Our studies showed that
both CCH3 and COH were formed during the reaction
(Figure 3). We could not detect any other oxygen-based
radicals, but they cannot be totally excluded because of other
Pd alloy nanoparticles (Table 1, entries 8–10). This observa-
ꢀ
tion is in line with synergistic effects of Au-Pd alloys obtained
with other substrates.[14–16,23,24]
More importantly,
a similar productivity, but with
improved methanol selectivity, was observed when using the
in situ generated H2O2 as compared to the experiments
performed with pre-formed H2O2 (0.5m; Table 1, entries 6
and 10). We considered that based on the gas-phase compo-
sition, the theoretical maximum amount of H2O2 which can be
formed under these conditions is about 250 mmol. Indeed, the
in situ method leads to a three-fold increase in reactivity as
compared to the reaction performed using low amounts of
preformed H2O2 (Table 1, entry 10, and Figure S3). Thus it is
clear that the use of oxygen is improved by adopting an in situ
capture approach. It has been previously shown that efficient
H2O2 synthesis can be performed at 28C with a similar
catalyst,[14,24] therefore we investigated the oxidation of
methane by using in situ generated hydrogen peroxide at
this temperature. The data (Table 1, entry 11) demonstrate
that Au-Pd supported nanoparticles generate the hydroper-
oxy species, as evidenced by the detection of H2O2 at the end
of the reaction, and also activate methane under these very
mild conditions. In addition, a higher selectivity for the
formation of methanol (about 80%) was achieved by
performing the reaction at 708C, but the overall oxygenate
productivity did not improve (Table 1, entry 12). Increasing
the H2 and O2 pressure, which should improve the amount of
H2O2 synthesized,[25,26] leads to an increase of methane
conversion and methanol formation (Table S5). Prolonging
the reaction time from 0.5 to 4 h is accompanied by an
enhancement of methanol formation from 0.24 to 2.02 mmol,
but longer reaction times also facilitates the conversion of
methanol to CO2 (Table S6). These results demonstrate that
there is the possibility of increasing the yield of methanol if
the contact time and reaction conditions are further opti-
mized.
We also used a soluble co-reductant, reduced nicotina-
mide adenine dinucleotide (NADH), with the AuPd catalyst,
and O2 to probe the efficiency of the -H use (Table 1,
entry 13). The total amount of products observed was about
half the amount of NADH added at the start of the
experiment. This data suggest that the system can also
achieve a high efficiency of -H use and that a water soluble
-H donor may be used in place of gas-phase H2.
In conclusion, we have shown that supported Au-Pd
catalysts can be effective for the oxidation of methane to
methanol using hydrogen peroxide as oxidant. The primary
product is methyl hydroperoxide which we consider is formed
from the reaction of H2O2 with CCH3.
Figure 3. Electron paramagnetic resonance (EPR) spectrum showing
radical species detected during the reaction of methane and H2O2 over
a 5 wt%Au-Pd/TiO2 (IW) catalyst with DMPO added to the reaction
mixture as the radical trapping agent. Key: black solid line: experimen-
tal signal, black dashed line: combined simulated signal for both COH
and CCH3 adducts, triangles: DMPO-OH adduct, and stars: DMPO-
CH3 adduct (aN and aH are the hyperfine coupling constants of the N
and H atoms).
factors relating to the experimental procedure employed,
especially since we have shown previously that Au-Pd/TiO2
catalysts produce superoxide species associated with the
titania support when exposed to organic peroxides.[23] Con-
sequently, we consider that the methane oxidation mechanism
for supported Au-Pd nanoparticles involves CCH3 and this is in
contrast to the reaction mechanism previously proposed for
methane oxidation using CuFe-ZSM-5 where CCH3 radicals
are not observed.[13] The termination reaction of methyl
radicals with hydrogen peroxide or COH would produce
methane or form methanol, respectively. Dissolved O2,
originating from hydrogen peroxide decomposition on the
catalyst surface, or a surface bound COOH may interact with
methyl radicals to form CH3OOC. We favor the latter
explanation due to the observation of methyl hydroperoxide
as the primary reaction product.
In subsequent experiments we considered that using
a hydroperoxy species generated in situ from molecular
oxygen may be beneficial for the reaction. As the 5 wt%
Au-Pd/TiO2 catalyst is very efficient for the synthesis of
H2O2,[24] we performed reactions using CH4, H2, and O2
diluted with N2 (0.86% of H2 and 1.72% of O2 in the reactor
gas feed) for the concurrent synthesis of in situ hydrogen
peroxide and eventual formation of methanol. Physical
mixtures of Au/TiO2 and Pd/TiO2, either in equimolar metal
amounts or the same metal weight percent, gave inferior
activity and selectivity compared to the titania-supported Au-
Received: September 24, 2012
Revised: November 23, 2012
Published online: December 11, 2012
Keywords: alloys · gold · methane · oxidation · palladium
.
[1] H. D. Gesser, N. R. Hunter, C. B. Prakash, Chem. Rev. 1985, 85,
235 – 244.
Angew. Chem. Int. Ed. 2013, 52, 1280 –1284
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
1283

.
Angewandte
Communications
[2] R. Pitchai, K. Klier, Catal. Rev. Sci. Eng. 1986, 28, 13 – 88.
[3] A. E. Shilov, G. B. Shulꢂpin, Chem. Rev. 1997, 97, 2879 – 2932.
[4] R. H. Crabtree, Chem. Rev. 1995, 95, 987 – 1007.
[5] J. H. Lunsford, Catal. Today 2000, 63, 165 – 174.
[6] K. Otsuka, Y. Wang, Appl. Catal. A 2001, 222, 145 – 161.
[7] D. Wolf, Angew. Chem. 1998, 110, 3545 – 3547; Angew. Chem. Int.
Ed. 1998, 37, 3351 – 3353.
[8] L. C. Kao, A. C. Hutson, A. Sen, J. Am. Chem. Soc. 1991, 113,
700 – 701.
[9] R. A. Periana, D. J. Taube, E. R. Evitt, D. G. Loffler, P. R.
Wentrcek, G. Voss, T. Masuda, Science 1993, 259, 340 – 343.
[10] R. A. Periana, D. J. Taube, S. Gamble, H. Taube, T. Satoh, H.
Fujii, Science 1998, 280, 560 – 564.
Taylor, D. W. Knight, C. J. Kiely, G. J. Hutchings, Science 2006,
331, 195 – 199.
[17] Y. Qiang, D. Weiping, Q. Zhang, Y. Wang, Adv. Synth. Catal.
2007, 349, 1199 – 1209.
[18] G. B. Shulꢂpin, T. Sooknoi, V. Romakh, G. Suss-Fink, L. S.
Shulꢂpina, Tetrahedron Lett. 2006, 47, 3071 – 3075.
[19] R. Raja, P. Ratnasamy, Appl. Catal. A 1997, 158, L7 – L15.
[20] For the homogeneous oxidation reactions the total amount of
metal used equaled the total amount of metal used in the
heterogeneous oxidation reactions with 2.5wt%Au-2.5wt%Pd/
TiO2 catalyst, 1 ꢁ 10ꢀ5 moles. These experiments were performed
to compare the possible catalytic activity of the homogeneous
Au or Pd metals under our typical reaction conditions.
[21] G. Sꢀss-Fink, G. V. Nizova, S. Stanislas, G. B. Shulꢂpin, J. Mol.
Catal. A 1998, 130, 163 – 170.
[11] R. Palkovits, M. Antonietti, P. Kuhn, A. Thomas, F. Schꢀth,
Angew. Chem. 2009, 121, 7042 – 7045; Angew. Chem. Int. Ed.
2009, 48, 6909 – 6912.
[12] A. B. Sorokin, E. V. Kudrik, D. Bouchu, Chem. Commun. 2008,
2562 – 2564.
[22] F. Bonino, A. Damin, G. Ricchiardi, M. Ricci, G. Spanꢃ, R.
DꢂAloisio, A. Zecchina, C. Lamberti, C. Prestipino, S. Bordiga, J.
Phys. Chem. B 2004, 108, 3573 – 3583.
[13] C. Hammond, M. M. Forde, M. H. Ab Rahim, A. Thetford, Q.
He, R. L. Jenkins, N. Dimitratos, J. A. Lopez-Sanchez, N. F.
Dummer, D. M. Murphy, A. F. Carley, S. H. Taylor, D. J. Willock,
E. E. Stangland, J. Kang, H. Hagen, C. J. Kiely, G. J. Hutchings,
Angew. Chem. 2012, 124, 5219 – 5223; Angew. Chem. Int. Ed.
2012, 51, 5129 – 5133.
[14] J. K. Edwards, B. E. Solsona, P. Landon, A. F. Carley, A.
Herzing, C. J. Kiely, G. J. Hutchings, J. Catal. 2005, 236, 69 – 79.
[15] D. I. Enache, J. K. Edwards, P. Landon, B. Solsona, A. F. Carley,
A. A. Herzing, M. Watanabe, C. J. Kiely, D. W. Knight, G. J.
Hutchings, Science 2009, 311, 362 – 365.
[23] M. I. Bin Saiman, G. L. Brett, R. Tiruvalam, M. M. Forde, K.
Sharples, A. Thetford, R. L. Jenkins, N. Dimitratos, J. A. Lopez-
Sanchez, D. M. Murphy, D. Bethell, D. J. Willock, S. H. Taylor,
D. W. Knight, C. J. Kiely, G. J. Hutchings, Angew. Chem. 2012,
124, 6083 – 6087; Angew. Chem. Int. Ed. 2012, 51, 5981 – 5985.
[24] J. K. Edwards, B. Solsona, E. Ntainjua, A. F. Carley, A. A.
Herzing, C. J. Kiely, G. J. Hutchings, Science 2009, 323, 1037 –
1041.
[25] M. Piccinini, E. Ntainjua, J. K. Edwards, A. F. Carley, J. A.
Moulijn, G. J. Hutchings, Phys. Chem. Chem. Phys. 2010, 12,
2488 – 2492.
[16] L. Kesavan, R. Tiruvalam, M. H. A. Rahim, M. I. Saiman, D. I.
Enache, R. L. Jenkins, N. Dimitratos, J. A. L. Sanchez, S. H.
[26] M. Piccinini, E. Ntainjua, J. K. Edwards, A. F. Carley, J. A.
Moulijn, G. J. Hutchings, Catal. Sci. Technol. 2012, 2, 1908 – 1913.
1284
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